Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.46   7.296%   $92.7681   $92.77   $92.75   $92.80  
  Purchase #2 $241.61   12.515%   $271.8475   $271.85   $271.85   $271.80  
  Purchase #3 $9.81   5.468%   $10.3464   $10.35   $10.35   $10.30  
  Purchase #4 $98.60   4.537%   $103.0735   $103.07   $103.05   $103.10  
  Purchase #5 $205.36   12.155%   $230.3215   $230.32   $230.30   $230.30  
  Purchase #6 $235.54   12.397%   $264.7399   $264.74   $264.75   $264.70  
  Purchase #7 $236.99   9.213%   $258.8239   $258.82   $258.80   $258.80  
  7 purchase totals = $1,114.37       $1,231.9208   $1,231.92   $1,231.85   $1,231.80